Discharges of lightning

Answer choices

1. A

   Too Strong: any6% picked this

   The highest point of any volcanic ash cloud will eventually exceed an altitude

   The author doesn't need to believe that all ash clouds exceed 5 km. They need to exceed that height in order for lightning discharge data to be a viable method of collecting data (since lightning doesn't start discharging until that height). But the author doesn't need to believe that lightning discharge data is always a viable method. He's only claiming that it's sometimes the only viable method. So he just has to assume that, "sometimes when weather radar (and any other means) is not available to measure ash cloud altitude, that ash cloud will exceed an altitude of 5 km".

   6%
2. B

   Correct83% picked this

   Lightning discharges can be detected in some regions in which weather

   Why this is right

   The author's argument boils down to this: "Sometimes lightning discharge data is our only source of data, because weather radar isn't available in all parts of the world." That is assuming that in some of those spots where weather radar isn't an option, lightning discharge data is. If we negated this, it would be saying "There is nowhere in the world where weather radar is unavailable yet lightning discharges can be detected". That negation totally kills the author's conclusion, so we know this answer needed to be assumed (the negation only needs to weaken the argument to be a correct answer, but the stronger the weakening the better).

   Skill tested: Necessary Assumption · how this choice captures the argument's function is the move to repeat next time.

   83%
3. C

   Out of Scope: regular clouds3% picked this

   Weather radar is no less accurate in determining the altitude of volcanic ash clouds than it is in determining

   Nothing in this argument has anything to do with measuring the altitude of regular clouds. The author isn't assuming anything about how weather radar's accuracy compares in different situations.

   3%
4. D

   Too Strong: likely6% picked this

   A volcanic ash cloud whose highest point exceeds an altitude of 5 kilometers is likely to be at least partly beyond

   There's no reason the author needs to assume that most ash clouds that exceed 5 km are at least partly beyond the reach of weather radar. The conclusion is only saying that sometimes lightning discharge data is our only chance at measuring altitude. The author needs to assume that some ash clouds that are beyond the reach of weather radar exceed 5 km (in order to believe that when weather radar is out of reach, lightning discharge data would potentially be an option).

   6%
5. E

   Out of Scope Comparison2% picked this

   Lightning discharges are no more frequent for large volcanic ash clouds than for small

   The argument is never talking about small vs. large clouds, so the author hasn't made any assumptions about that sort of comparison. We know that lightning discharges become more frequent the higher the ash cloud moves above 5 km, but that's the height of the cloud, not the size. If we were equating height with size, then we'd say the author's argument more or less contradicts this answer, since the higher ones have more frequent discharges.

   2%